Re: [Discuss-gnuradio] TX characterisation of USRPN210 with SBX daughterboard

[Martin Braun]

On 03/24/2014 05:44 PM, Gayathri Ramasubramanian wrote:
> Thanks for looking into my post.
> I used a cable to connect to the spectrum analyzer ( united microflex
> 150 with 15 db/ft attenuation, my cable length was 1 ft). However before
> connecting to the spectrum analyzer, I had an attenuator set to 50 dB.
> These readings were taken with a gain set to zero. I used *tx_waveforms*
> program provided in the examples with:
> BB freq: 6.25MHz
> Sampling rate : 13 MHz

BTW, that's an unusual sampling rate... are you running off of your own
clock?
Still, the differences are pretty big. I'm not surprised to see less for
the higher frequency, but the magnitude does surprise me.

> I just varied my amplitude in these steps.

Can you play around with the gain (say, set it to mid-point in dB) and
see if the differences are still that big?

M

> 
> Thanks
> Gayathri 
> 
> On Mar 24, 2014, at 11:22 AM, "Martin Braun-2 [via GnuRadio]" <[hidden
> email]> wrote:
> 
>> On 03/24/2014 05:56 AM, Gayathri Ramasubramanian wrote:
>> > I am trying to characterize the TX and RX characteristics of USRPN210
>> > with a SBX board. I have tried one test : Amplitude Variation
>> > effects, by varying the amplitude in steps and finding out the o/p
>> > power through spectrum analyser. The foll are the readings I got.
>> > Amplitude level 921.25 MHz 2.45625 GHz 0.0625 -49.18 -60.97 0.125
>> > -43.2 -55.05 0.25 -37.25 -49.09 0.5 -31.24 -43.05 1 -25.38 -37.13
>> > Amplitude change 921MHz 2.456GHz 1 to 0.5 5.86 5.92 0.5 to 0.25 6.01
>> > 6.04 0.25 to 0.125 5.95 5.96 0.125 to 0.0625 5.98 5.92
>>
>> Gayathri,
>>
>> how did you measure? Did you use an antenna, or cable connection to the
>> spectrum analyzer?
>> Also, what were your gain settings? And your tx signal?
>>
>> Martin
>>
>> > when i ploted the graph in excel, (O/p power Vs amplitude), i got two
>> > almost linear curves, but their was a big difference in the 2 lines @
>> > 921.25 MHz and 2.45625 GHz (as seen above) at the start and if
>> > extrapolated could converge at a higher ampl and o/p power. I was not
>> > sure about my results and was looking to see if some one could let me
>> > know if these values look within the normal expected behaviour? if
>> > not, please let me know what is the normal expected behaviour. I am
>> > new to USRP and GRC programming and doing this for a project.